During filling of the chambers defined between filter plates of a filter press, sensing when the feed pump slows down or stops so as to initiate a pressure step-up in the air supplied to the feed pump has presented a significant problem. Although a position or motion sensor mounted directly on the feed pump would solve this problem, many users prefer to utilize different types of feed pumps, and the many different types of available feed pumps prevent the adoption of any standardized sensing arrangement mountable directly on the feed pump. Thus, there is a need to be able to sense the slow down or intermittent stoppage of the feed pump without having to rely on a sensor which mounts directly on the pump. In addition, there is a need for a sensor capable of detecting the slow down of the feed pump and which may be utilized with both small and large capacity feed pumps.
In an effort to solve the above-described problem, flow sensors of the paddle wheel type and of the type including a movable ball in a tapered column have been employed and are typically mounted in the air supply line leading to the feed pump. However, these devices have been found to be unreliable, and in this regard, breakage of the paddle wheel type device has been encountered.
In addition, an in-line flow sensor has been employed which includes an outer tube having a slightly tapered inner diameter, and a spring-urged piston slidably disposed therein. However, with this arrangement, the large stroke of the piston presents problems with regard to the anticipated mode of operation.
It is therefore an object of the present invention to provide an improved device and method for filling a filter press which overcomes many of the disadvantages associated with prior arrangements.
More specifically, one aspect of the invention relates to a filter press including a horizontally elongate frame, and first and second head assemblies mounted at opposite ends of the frame, wherein the first head assembly is disposed adjacent one end of the frame and supported for horizontal movement toward and away from the second head assembly so as to be respectively movable into closed and opened positions, and the second head assembly is stationarily positioned adjacent the other end of the frame. A plurality of filter plates are supported on the frame for movement therealong between the first and second head assemblies, the filter plates being pushed together into a horizontally extending closed stack and clampingly held between the first and second head assemblies when the first head assembly is moved toward the second head assembly into the closed position. A diaphragm-type feed pump is typically provided for supplying slurry material under pressure to the plurality of chambers defined between the filter plates. The feed pump is connected to a source of air by an air supply line, and is exhausted with an exhaust line in communication with the atmosphere. A pressure regulator is associated with the air supply line for maintaining the air supplied to the feed pump at a predetermined pressure. The press also includes an air flow sensor adapted to detect a decrease in air flow volume therethrough upon slowing of the feed pump during a press filling cycle and to transmit a signal to a controller associated with the pressure regulator to increase the pressure of the air supplied to the feed pump.
Another aspect of the invention relates to a flow control sensor including a housing having an inner wall defining an interior chamber, and a piston slidably disposed within the chamber and defining a flow passage therein. The piston is movable between an open position for permitting air flow through the flow passage and a closed position for closing off the flow passage, and has a magnet mounted thereon for movement therewith. The sensor additionally includes a switching device mounted on the housing and adapted to detect an axial position of the magnet as the piston approaches the closed position upon slowing of the feed pump during a press filling cycle, and to transmit a signal to increase the pressure of the air supplied to the feed pump. The switching device is also adjustable to accommodate air flow through the sensor proportional to the capacity of the feed pump.
Still another aspect of the invention relates to a method for filling a filter press having a feed pump for supplying slurry material under pressure to a plurality of chambers defined by filter plates, a pressure regulator associated with an air supply line connected to the feed pump, and a controller for operating the pressure regulator. The method includes: (1) providing an air flow sensor in the air supply line between the feed pump and the pressure regulator, the air flow sensor having a piston including a flow passage therethrough and being movable between open and closed positions; (2) adjusting the air flow sensor to sense a closing movement of the piston and thus a decrease in air flow volume through the air flow sensor proportional to the feed pump capacity; (3) supplying pressurized air to the feed pump through the air flow sensor by moving the piston thereof into the open position and feeding slurry into the filter press; (4) performing step (3) until the slurry pressure in the filter press approaches the supply pressure and causes the piston of the air flow sensor to move from the open position toward the closed position; (5) sensing the position of the piston as same approaches the closed position, and before the piston fully closes transmitting a signal to the controller to increase the supply pressure to the feed pump; and (6) repeating steps (3) through (5) at the increased supply pressure until a predetermined maximum supply pressure is reached.
Yet another aspect of the invention relates to a method for filling a filter press having a feed pump for supplying slurry material under pressure to a plurality of filter plates, a pressure regulator associated with an air supply line connected to the feed pump, a controller for operating the pressure regulator, and an exhaust line connected to the feed pump. The method includes: (1) providing an air flow sensor in the exhaust line, the air flow sensor having a piston including a flow passage therethrough, the piston being movable between open and closed positions and being normally biased into the closed position; (2) adjusting the air flow sensor to sense a closing movement of the piston and thus a decrease in air flow volume through the air flow sensor proportional to the feed pump capacity; (3) supplying pressurized air to the feed pump through the air supply line and feeding slurry into the filter press; (4) supplying a pressurized air pulse generated by the feed pump to the exhaust line to move the piston of the air flow sensor into the open position, and thereafter returning said piston to said closed position; (5) repeating steps (3) and (4) until the piston remains in the closed position for a period of time greater than a predetermined time period and thereafter transmitting a signal to the controller to increase the supply pressure to the feed pump.
Other objects and purposes of the invention will be apparent to persons familiar with devices of this general type upon reading the following specification and inspecting the accompanying drawings.